n.

1. 間諜；密探[C]
   She liked the adventures of a spy.

   她喜歡間諜的冒險。

2. 暗中監視，暗中偵察[U]

vi.

1. 當間諜；暗中監視；刺探[（+on/upon/into）]
   We spied on the man.

   我們監視那個人。

vt.

1. 暗中監視；偵察出
   He sent out a party to spy the enemy.

   他派出一個小分隊暗中監視敵人的行動。

2. 察覺，發現[O4]
   We spied a stranger hanging around the corner.

   我們發現一位陌生人在拐角處閒蕩。

   He was the first to spy the triangle fin of a shark coming towards us.

   他第一個發現一條鯊魚的三角形鰭向我們游來。

3. 仔細察看
   The visitors spied the exhibits at the fair.

   參觀者細細察看展覽會上的陳列品。

n.

1. a person employed by a government or other organization to collect and report secret information on an enemy or competitor.
2. a person who observes others secretly.

v.

1. be a spy.
   ▸ (spy on) observe furtively.
2. observe or notice.